2249
Organometallics 1987,6, 2249-2250
The Clalsen Rearrangement of Iron Allyloxy Carbene Complexes
Scheme I
Anthony 0. M. Barrett' and Nancy E. Carpenter Scheme I1
Department of Chemistry, Northwestern University Evanston, Illinois 60208 Received April 2 I , 1987
c,
Fe-CPR:
Summary: Several cationic iron(I I) allyloxy carbene complexes have been prepared from the corresponding iron vinylidenes (Fe(q5-C5H5)(CO)[P(OCH,),] (C= CR'R2)'X- (X = BF, OSO,CF,). These compounds have been deprotonated with KH and 18-crown-6 and thermally rearranged in situ to give the corresponding y,d-unsaturated iron acyl complexes in moderate yields.
Metal vinylidene complexes have been the subject of considerable recent Mononuclear vinylidene complexes such as 1 undergo reactions which include deprotonation a t the P-carbon (to give the ubonded acetylide),?,and dimerization.4~~However, the key characteristic of these complexes is the extremely electrophilic a-carbon (13CNMR 6 320-380).2 In most cases, the addition of nucleophiles to this center occurs with ease, resulting in formation of the corresponding carbene complexes 2 (Scheme Since the metal moiety in 2 can be oxidatively cleavede to give the corresponding carbonyl compound, vinylidene complexes can be envisioned as organometallic ketene surrogates. The chemistry of transition-metal acyl complexes is complementary in that oxidative demetalation can be used to produce the corresponding carboxylic acid, ester, or amideag Metal acyls have found widespread use in organic synthetic methodology since electrophilic functionalization of the derived enolate anions can be used to readily produce extended carbon frameworks. Such acyl anion chemistry is particularly useful in that spectacular stereochemical control can be observed when the metal center is asymmetric.1° In contrast, the use of vinylidene intermediates to stereoselectively elaborate organic molecules has been completely
(1)The first transition-metal vinylidene complex, containing a bridging vinylidene ligand in a diiron complex, was obtained in 1966 Mills, 0. S.;Redhouse, A. D. J. Chem. SOC., Chem. Commun. 1966,444; J. Chem. Soc. A 1968,1282. (2)For an excellent review of vinylidene (and propadienylidene) metal complexes, see: Bruce, M. I.; Swincer, A. G. Adu. Organomet. Chem. 1983,22,59. (3)Davison, A.; Selegue, J. P. J. Am. Chem. SOC.1978, 200, 7763. Bruce, M. I.; Wallis, R. C. Aust. J. Chem. 1979,32,1471.Bruce, M. I.; Wong, F. S.; Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1982,2203. (4)Davison, A.; Solar, J. P. J. Organomet. Chem. 1978,155,C8. (5)Boland-Lussier, B. E.; Hughes, R. P. Organometallics 1982,1,635. (6)For examples see: Davison, A.; Selegue, J. P. J. Am. Chem. SOC. 1980,102,2455.Berke, H. 2.Naturforsch, B: Anorg. Chem., Org. Chem. 1980,35B,86. Adams, R. D.; Davison, A,; Selegue, J. P. J. Am. Chem. SOC. 1979,101,7232. Bruce, M. I.; Wallis, R. C. J. Organomet. Chem. 1978,161,C1. Bruce, M. I.; Swincer, A. G.; Wallis, R. C.J. Organomet. Chem. 1979,171,C5. Bruce, M. I.; Swincer, A. G. Aust. J. Chem. 1980, 33, 1471. Selegue, J. P. J . Am. Chem. SOC. 1982,104,119. (7)Boland-Lussier, B. E.;Hughes, R. P. Organometallics 1982,1,628. (8) Barrett, A. G. M.; Sturgess, M. A. TetrahedronLett. 1986,27,3811; J. Org. Chem. 1987,52,3940. (9)Aktogu, N.;Felkin, H.; Baird, G. J.; Davies, S. G.; Watts, 0. J. Organomet. Chem. 1984,262,49. (10)For examples see: Theopold, K. H.; Becker, P. N.; Bergman, R. G. J. Am. Chem. SOC.1982,104,5250.Liebeskind, L. L.; Welker, M. E.; Fengl, R. W. Zbid 1986,108,6328and references therein. Davies, S.G.; Dordor-Hedgecock, I. M.; Warner, P.; Jones, R. H.; Prout, K. J. Organomet. Chem. 1985,285,213. Rusik, C. A.; Tonker, T. L.; Templeton, J. L. J. Am. Chem. SOC. 1986,108,4652.
r
CH R'R'
-
R'
(H BF,.Et ,O) Tf.0 Et,O
R'
1"96%-
[L,Fe=C=CR'R']'X-
1
-
1. KH 18-crown-6
I,Fe=C'o"'Ri 'CHR'R'
RT
4
X-
C,H,,
O°C
5
R'
6
1
neglected. Indeed even the application of metal vinylidenes in synthetic methodology has remained relatively unexplored. However recent research efforts in this laboratory have demonstrated that vinylidene complexes are especially useful in the synthesis of 0-1actams.S Herein we report the reaction of cationic iron(I1) vinylidenes with allylic alcohols and the subsequent deprotonation and Claisen rearrangement1' of the resulting allyloxy carbene complexes. The synthetic sequence leading to the rearrangement products 7 is illustrated with the unsubstituted vinylidene complex 4b (R' = R2= H, R5 = OCH,, X = BF,; Scheme 11). This compound was prepared from the corresponding iron acyl complex 3b12by dehydration with tetrafluoroboric acid (2.5 equiv) and trifluoromethanesulfonic anhydride (3 equiv) according to the general procedure of Boland-Lussier and hug he^.^ The vinylidene, although characterized by 'H NMR [(CDCl,, 90 MHz) 6 3.64 (d, 9 H, J = 12 Hz), 5.33 (s, 5 H), 5.37 (d, 2 H, J = 3 Hz)] ,was not isolated but instead was condensed directly with allyl alcohol by using standard Schlenk techniques13 to give the cationic allyloxy carbene complex 5b [lH NMR (CDCl,, 90 MHz)G 3.05 (s, 3 H), 3.78 (d, 9 H, J = 12 Hz), 5.10 (s, 5 H), 5.18 (s, 2 H), 5.39-5.70 (m, 2 H), 5.92-6.32 (m, 1 H)].Deprotonation of 5b with KH and 18-crowr1-6~~ gave the neutral iron vinyl allyl ether 6b,15 which was thermally rearranged in situ in refluxing benzene to give the desired y,6-unsaturated acyl complex 7b16 ['H NMR (CDCl,, 400 MHz) 6 2.14 (m, 2 H), 2.93 (m, 2 H), 3.63 (d,
(11)For recent reviews on the Claisen rearrangement, see: Rhoads, S. J.; Raulins, N. R. Org. React. (N.Y.) 1975,22, 1. Bennett, G. B. Synthesis 1977,589. Ziegler, F. E.Acc. Chem. Res. 1977,10,227. (12)Wilkinson, G.; Piper, T. S. J. Inorg. Nucl. Chem. 1966,3,104. Green, M.; Westlake, D. J. J. Chem. SOC.A 1971,367. (13)Shriver, D. F. Manipulation of Air-Sensitive Compounds; McGraw-Hill: New York, 1969. (14)Buncel, E.;Menon, B. J. Am. Chem. SOC. 1977,99, 4457. (15)For examples of related iron vinyl complexes see: Reger, D. L.; Belmore, K. A. Organometallics 1985,4,305.Reger, D. L.; Swift, C. A. Organometallics 1984,3,876.Reger, D. L.;Mintz, E.; Lebioda, L. J. Am. Chem. SOC. 1986,108, 1940. Reger, D. L.; Belmore, K. A.; Mintz, E.; McElligot, P. J. Organometallics1984,3,134.Reger, D. L.; Klaeren, S. A.; Lebioda, L. Organometallics1986,5,1072.GrBtach, G.; Malisch, W. J. Organornet. Chem. 1983,246,C42,C49. Davison, A.; Reger, D. L. J. Am. Chem. SOC.1972,94,9237.GrBtach, G.; Malisch, W. J. Organomet. Chem. 1984,262,C38. (16)All rearrangement products were fully authenticated by spectral data and microanalyses or high-resolution mass ion measurements.
0276-7333187f 2306-2249$01.50f 0 0 1987 American Chemical Society
2250
Organometallics 1987, 6, 2250-2252 Table I. Summars of Rearrangement Results product
entrv
carbene comolex
soh
t e m n "C time. h
(%)"
68
120
7a
118-120
24
7b (33)
114
25
7c (22Y
reflux
26
7d (60Id
76-78
26
7e (13Ie
reflux
26
7f (3411
reflux
21
7g (21)
reflux
20
9 (28)
Yield calculated from the starting saturated iron acyl complex 3, unless otherwise noted. Yield calculated from the allyloxy carbene complex 5. Product obtained as a 3:l mixture of diastereomers. dProduct obtained exclusively as the E isomer. eProduct obtained as a 1:l mixture of diastereomers. fproduct obtained as a complex mixture of diastereomers.
9 H, J = 12 Hz), 4.63 (s, 5 H), 4.87 (d, 1 H, J = 9.2 Hz), 4.94 (dd, 1H, J = 16.8, 1.6 Hz), 5.75 (m, 1 H)]. Further results are summarized in Table I. It is clear from these examples that a range of simple allylic alcohols (and propargyl alcohol, entry 8) indeed reacted with the cationic iron vinylidenes 4 to produce the desired carbene complexes, and these in turn gave the corresponding rearrangement products 7. The overall yields from the starting acyl 3 were modest (10-60%)." However the method is clearly useful for the preparation of diverse systems including the sterically encumbered product 7g (entry 7) and the allene 9 (entry 8). The allene 9 readily isomerized to produce the corresponding diene acyl complex 10. In
9
10
principle these y,d-unsaturated iron acyls 7 should be available from direct allylation of the enolate derived from 3. Indeed this method has been efficiently wed to prepare 7a,9but attempts to apply this strategy to the preparation
(17) Approximately 5-30% of the starting saturated acyl complex 3 was typically recovered.
of the trimethyl phosphite substituted iron acyls failed due to competitive metalation of the cyclopentadienyl ring.18J9 Thus the Claisen rearrangement provides a valuable route to the y,d-unsaturated iron acyls when the alternate alkylation route presents a problem. In conclusion, these results demonstrate that iron allyloxy carbene complexes, on deprotonation, undergo a [3,3] sigmatropic rearrangement to give the corresponding y,d-unsaturated acyl complexes. Further studies are in progress to confirm the intramolecular nature of the rearrangement and to optimize the yield and diastereoselectivity of the transformation. Absolute stereochemical control of the Claisen rearrangement via organometallic intermediates would be a reaction of considerable synthetic importance. Acknowledgment. We thank the National Science Foundation (CHE-8500890) for the generous support of this program and the Midwest Center for Mass Spectrometry, an NSF Regional Instrument Facility (CHE8211164), for obtaining mass spectral data. Supplementary Material Available: Spectroscopic and microanalytical data characterizingvinylidenes, carbenes, and acyls described in this paper (6 pages). Ordering information is given on any current masthead page. (18) Sturgess, M. A., unpublished results. (19) Heah, P. C.; Patton, A. T.; Gladysz, J. A. J.Am. Chern. SOC.1986, 108. 1185.
Thermal Rearrangement of (S ,S)-1-NaphthylphenylmethyI( l-ch1oroethyl)silane and (S )-( l-Chloroethyl)phenyldimethylsilane Gerald L. Larson,"' Rlcardo Klesse,lband Frank K. Cartledgelc Department of Chemistry, University of Puerto Rico Rio Piedras, Puerto Rico 00931 Department of Chemistry Louisiana State University Baton Rouge, Louisiana 70803 and Petrarch Systems, Bartram Road Bristol, Pennsylvania 19007 Received March 12, 1987
Summary: (S ,S )-1-NaphthylphenylmethyI(l-chloroethy1)silane (1)and (S)-( l-chloroethyl)phenyldimethylsilane (2) were prepared and employed in a study of the stereochemistry of their thermal rearrangements. Although the stereochemistry at silicon could not be determined due to racemization, the stereochemistry at carbon was found to be inversion with a high degree of stereospecificity. The stereochemistry at carbon is preserved in a subsequent oxidative cleavage of the Si-C bond providing an interesting silicon-mediated preparation of (S )- l-phenylethanol and (S)-l-( l-naphthy1)ethanol.
The rearrangement of a-haloorganosilanes has been shown to take place under thermali2 Lewis acid ~atalyzed,~ (1) (a) University of Puerto Rim and Petrarch Systems. (b) University of Puerto Rico. (c) Louisiana State University. Taken in part from the Ph.D. Thesis of R.K., UPR, Rio Piedras, P.R., 1987.
0 1987 American Chemical Society
